(1) Field of the Invention
The present invention relates to an energy absorber system for an undercarriage, and to an aircraft provided with said energy absorber system.
(2) Description of Related Art
Conventionally, an aircraft has landing gear via which it stands on the ground. For example, the landing gear may be provided with three or four wheeled undercarriages constituting a support polygon for the aircraft on the ground. Undercarriages are also known that are provided with skids.
Such undercarriages may be retractable in order to improve the aerodynamic drag of the aircraft. The most pre-eminent elements of the aircraft are folded into the inside of the fuselage, in particular when retractable landing gear is used. More precisely, while in flight, each undercarriage is retracted into a compartment that is conventionally referred to as a “wheel bay”, so as to be ready for deploying at the appropriate moment while landing.
Civil certification regulations, e.g. known under the acronyms “FAR”, “JAR”, or “EASA-CS” (short for European Aviation Safety Agency Certification Specification) require undercarriages to present certain levels of dynamic energy absorption.
Thus, according to those civil certification regulations, for an aircraft having a first predetermined vertical speed on impact with the ground, an undercarriage must be capable of absorbing the kinetic energy of the impact without suffering any permanent deformation of the components making up the undercarriage, with this being required for various attitudes of the aircraft while landing, and for the most unfavorable weight and centering conditions. Similarly, when the aircraft presents a second predetermined vertical impact speed against the ground that is greater than the first speed, each undercarriage must absorb the kinetic energy of the impact without rupturing the components making up the undercarriage, with this being required for various attitudes of the aircraft while landing, and for the most unfavorable weight and centering conditions.
Under such circumstances, an undercarriage that complies with civil certification regulations is referred to for convenience as a “standard” undercarriage, and it often includes a shock absorber of a first type, referred to, for convenience, as a “first” shock absorber.
For example, a standard undercarriage may be provided with a rocker arm extending from a first end zone towards a second end zone supporting one or more wheels, the first end zone being hinged to a first flank of a wheel bay.
Furthermore, the undercarriage includes an energy absorber system provided with a first shock absorber of the oleopneumatic type. The first shock absorber is hinged firstly to the rocker arm and secondly to a second flank of the wheel bay. The first shock absorber may be substantially vertical, i.e. directed in a direction that is substantially perpendicular to the ground when the aircraft is standing on the ground, and substantially parallel to the first and second flanks. This position of the shock absorber may nevertheless be oriented in some other way (i.e. non-vertical) for reasons of integration and/or compatibility with the structure to which it is to be connected.
One such first shock absorber comprises a piston sliding in a main cylinder having a head that is in contact with a first chamber that is filled with oil and that is fitted with throttling orifices serving to absorb energy during a landing. In addition, the shock absorber has a second chamber filled with gas in order to support the aircraft in a static situation. The second chamber communicates with the first chamber, the second chamber having a volume that is reduced when the first shock absorber is compressed in order to contribute to absorbing energy during a landing.
The first shock absorber may optionally also enable the rocker arm to be retracted into the wheel bay.
Document FR 2 684 957 describes such a standard undercarriage.
Those standard undercarriages are most effective and they serve to satisfy the requirements of civil certification regulations.
Nevertheless, it can be understood that standard undercarriages are sometimes not adapted to vertical ground impact speeds that are greater than the speeds defined by the civil regulations.
Furthermore, in addition to civil certification regulations, there exist military qualification regulations known for example under the name “MIL-STD-8698”, naval qualification requirements known for example under the name “AR56”, and military crash qualification requirements known for example under the name “MIL-STD-1290”, which are more severe than civil certification regulations.
These military and naval qualification regulations “MIL-S-8698” and “AR56” impose vertical speeds that are greater than the above-mentioned first and second vertical speeds. The military crash qualification regulations “MIL-STD-1290” impose even greater vertical speeds than those mentioned above and they define the behavior of undercarriages in terms of energy absorption and integrity up to the fuselage making contact with the ground.
Undercarriages adapted to military, naval, and military crash qualification regulations are referred to for convenience as “high energy absorption” undercarriages. By way of example, a high energy absorption undercarriage differs from a standard undercarriage by often including an energy absorber system that is provided with a shock absorber of a second type, that is referred to for convenience as a “second” shock absorber. That second shock absorber is provided with a piston having an available stroke that is longer than the stroke of a first shock absorber of a standard undercarriage.
Furthermore, a second shock absorber of a high energy absorption undercarriage may, in particular, have multiple chambers filled with gas and varying throttling orifices.
The second shock absorber of a high energy absorption undercarriage is therefore often bulkier, heavier, and more expensive than the first shock absorber of a standard undercarriage.
Control of the forces generated by the second shock absorber may be incorporated in a first shock absorber via multiple or varying throttling orifices without significant penalty in terms of cost or weight. However, the long stroke of the piston gives rise to an increase in the size of the wheel bay and to the attachment points of the shock absorber being further away, thereby giving rise to large amounts of extra cost and weight. Furthermore, increasing the size of the wheel bay is not always possible for reasons of integration and/or compatibility with other items of equipment.
It should be observed that document FR 2 885 596 presents an undercarriage having a rocker arm and brake means for the rocker arm.